The Athel tamarisk has ingenious ways of surviving in a dry climate
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An evergreen desert shrub commonly found in the Middle East has developed a unique strategy to absorb moisture from the air. It excretes salt crystals onto its leaves, which might aid in the absorption process.
According to Panče Naumov from New York University Abu Dhabi, “Not only does the plant use some water, it can gain some water.”
The Athel tamarisk (Tamarix aphylla) belongs to a group of plants called recretohalophytes, which are specially adapted to survive in extremely salty soils. These plants absorb saline water through their roots, utilize it for nourishment, and then excrete the concentrated saltwater onto their leaves.
Naumov and his team were intrigued by what happens to the water after it is excreted. Initially, they theorized that the droplets might irrigate the plant’s roots. However, upon close observation through time-lapse videos, they discovered that the droplets adhere to the leaf’s surface instead of falling. “The droplets do not actually fall at all. They stick to the surface,” explains Naumov.
To investigate further, the researchers collected salt samples from the tamarisk leaves at different times of the year, taking into account seasonal variations. X-ray analysis revealed that the samples were mostly composed of sodium chloride, along with more than ten other salt compounds.
To test how the salt adheres to the leaf’s surface, the team created a model using wax extracted from the plant. They found that while larger crystals easily fell off the waxy surface, smaller lithium sulphate crystals remained stuck. The salt with lithium sulphate crystals demonstrated a wider range of water absorption across various humidity levels compared to pure sodium chloride. The researchers used dyed water to track how the salty liquid on the leaf’s exterior diffused into the plant.
Naumov suggests that this indicates the plant may have two mechanisms for obtaining water from salty soils. During hotter and drier days, it takes in water through its roots. Then, during cooler and more humid nights, it utilizes the excreted salts on its leaves to absorb water. “They work in synergy, day and night,” Naumov adds.
Maheshi Dassanayake from Louisiana State University finds this hypothesis plausible, although she is skeptical about the researchers’ evidence regarding how the plant uses the water absorbed by the salt on its leaves. “I’m missing the mechanistic basis for how the plant uses energy to obtain the water,” she remarks.
Even if the plant does not utilize the water gathered by salt in this manner, Naumov suggests that the salt compounds could have applications in systems that harvest water from the air or for cloud seeding to induce rainfall.
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